Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor. A housing supports the drive motor and head actuator and surrounds the head and disk to provide a substantially sealed environment for the head-disk interface.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a relatively fragile suspension that connects the slider to the actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is "self-loaded" to the disk surface by means of a "negative-pressure" air-bearing surface on the slider. Contact start/stop (CSS) disk drives operate with the slider in contact with the disk surface during start and stop operations when there is insufficient disk rotational speed to maintain the air bearing. In contrast to CSS disk drives, "load/unload" disk drives mechanically unload the slider from the disk when the power is turned off, typically by means of a ramp which contacts the suspension when the actuator is moved, and then load the slider back to the disk when the disk has reached a speed sufficient to generate the air bearing. Both types of disk drives maintain a relatively thin lubricant film on the disk surface to prevent damage to the head and disk caused by any contact between the head and disk.
It has been known since the early days of magnetic recording that minimizing the head-disk spacing is desirable because the amplitude of the read signal from the disk increases with decreasing head-disk spacing. Higher recording densities can thus be achieved. In conventional, commercially available air-bearing disk drives the minimum achievable head-disk spacing is typically between 1000-2000 Angstroms. In addition, this spacing is not maintained constant, but varies with disk radius because the air velocity beneath the air-bearing slider is directly proportional to the relative velocity of the disk beneath the slider. To both minimize the head-disk spacing and to maintain it constant with disk radius, liquid bearings have been proposed as possible alternatives to the conventional air bearing at the head-disk interface in magnetic recording disk drives. For example, in assignee's pending application, U.S. Ser. No. 264,604, filed Oct. 31, 1988, and published May 9, 1990, as European published application EP 367510, a disk drive is described which uses a continuously recirculating, low-viscosity liquid lubricant which is maintained as a relatively thick layer on the disk, and a transducer carrier that has triangular-shaped feet to plow through the low-viscosity liquid layer. The EP 367510 reference suggests that a head-disk spacing of approximately 500 Angstroms can be obtained with a liquid film having a thickness of approximately 10,000 Angstroms. Similarly, in U.S. Pat. No. 5,097,368 assigned to Conner Peripherals, filed Dec. 20, 1989, and issued Mar. 17, 1992, a recirculating liquid-bearing disk drive is described in which a head-disk spacing of approximately 300-700 Angstroms can be achieved at the operating speed of a conventional air-bearing disk drive if a load of approximately 45 grams is applied to force the head carrier against the liquid bearing (see FIG. 6 of the '368 patent).
In U.S. Pat. No. 4,901,185 assigned to Toshiba, filed in the U.S. on Jul. 10, 1986, and issued Feb. 13, 1990, the problems of minimizing and maintaining constant the head-disk spacing are addressed by a disk drive which uses a combined air and liquid bearing to support the transducer carrier. An air-bearing slider provides support for the forward portion of the carrier while the rear portion, which includes the magnetic head, contacts and is supported by a conventional liquid lubricant film. The '185 patent suggests that a head-disk spacing of less than approximately 800 Angstroms can be achieved using a lubricant film of greater than approximately 200 Angstroms thickness.
More recently, in assignee's U.S. Pat. No. 5,202,803, filed Jul. 2, 1991, and issued Apr. 13, 1993, a disk drive is described in which a conventional nonrecirculating, high-viscosity lubricant film is maintained on the disk and the transducer carrier is a modified three-rail air-bearing slider that has a rear "ski" pad. When the disk drive reaches operating speed, the air-bearing effect of the slider rails provides the primary support for the carrier, while the rear ski pad, which supports the magnetic head, contacts the lubricant film. The thickness of the lubricant film on the disk is approximately 20-100 Angstroms, which would also be the approximate head-disk spacing between the rear pad and the disk surface, assuming a perfectly smooth disk surface.
While liquid-bearing disk drives present the opportunity for closer head-disk spacing than air-bearing disk drives, they also present several difficulties. The carrier must provide a low-static friction ("stiction") interface when the carrier is at rest on the disk because liquid-bearing disk drives have thicker lubricant films and smoother disks than air-bearing disk drives. The carrier must also be designed to create small drag through the liquid film and to minimize liquid depletion from the disk. In addition, the carrier must be able to perform adequately over a wide range of relative carrier-disk velocities which occur at different disk radii.
What is needed is a disk drive with an improved head-disk interface that takes advantage of an air bearing to avoid the problems associated with liquid bearings, yet provides a head-disk spacing that is significantly less than even that achievable by a liquid bearing, and is less sensitive to variation with disk radius and to variations in head-carrier manufacturing parameters.